TGFbeta may potentially be successful in the treatment of epithelial cancers since it inhibits the proliferation of responsive carcinoma cells and elicits differentiation-like effects. However, many poorly- differentiated or highly-aggressive colon carcinoma cells are unresponsive to the growth inhibitory effects of TGFbeta. Alterations in TGFbeta signaling components likely represent major mechanisms underlying defects in TGFbeta responsiveness, yet little is known regarding TGFbeta signaling pathways, even in untransformed epithelial cells. The overall goal of this proposal is to identify TGFbeta signaling proteins in untransformed intestinal epithelial (IEC) 4-1 cells that bind the cytoplasmic domain of the type I TGFbeta receptor (RI) or that directly interact with the type II TGFbeta receptor (RII). The cDNA's isolated will be functionally characterized, in part, using the cell culture model systems for sensitivity and resistance to TGFbeta that were previously established as part of the grant for which this is the competing continuation. These model systems consist of: (l) MOSER human colon carcinoma clones that display isoform-specific sensitivity or resistance to TGFbeta1 and TGFbeta2, (2) TGFbeta-responsive, well- differentiated versus TGFbeta-unresponsive, poorly-differentiated human colon carcinoma cell lines, and (3) TGFbeta-sensitive and -resistant untransformed intestinal epithelial clones. The functional characterization of cDNA's will include: (1) sequence comparisons by GenBank analysis, (2) identification of sequence mutations in human colon carcinoma cells and/or TGFbeta-resistant cells, (3) verification of protein phosphorylation by, or interaction with TGFbeta receptors, and (4) determination of differences in protein levels (or activities) between TGFbeta-resistant and sensitive cells, and between untransformed and carcinoma cells. The results obtained from this proposal will identify targets for the development of drugs that will either mimic the inhibitory effects of TGFbeta in epithelial cells or that will eliminate the development of resistance to growth regulation by TGFbeta.